Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $85.41   10.113%   $94.0475   $94.05   $94.05   $94.00  
  Purchase #2 $94.88   7.444%   $101.9429   $101.94   $101.95   $101.90  
  Purchase #3 $189.50   7.727%   $204.1427   $204.14   $204.15   $204.10  
  Purchase #4 $69.65   11.113%   $77.3902   $77.39   $77.40   $77.40  
  Purchase #5 $103.42   4.676%   $108.2559   $108.26   $108.25   $108.30  
  Purchase #6 $147.65   5.485%   $155.7486   $155.75   $155.75   $155.70  
  Purchase #7 $47.43   11.815%   $53.0339   $53.03   $53.05   $53.00  
  7 purchase totals = $737.94       $794.5617   $794.56   $794.60   $794.40